The present invention relates generally to a guardrail assembly for highways and particularly to a wood clad crash barrier wherein the cladding acts as lubricant between an impacting object and the barrier.
The present invention addresses problem issues with the prior art guardrail and posts, such as reducing friction between an impacting vehicle and the prior art highway crash barriers, providing potential additional structural strength to individual structural members of the prior art crash barriers and support posts, allowing the use of a wood exterior appearance without the need to use potentially environmentally harmful wood preservative treatment, and providing an improved visibly pleasing external appearance for prior art guardrail and posts.
The primary function of guardrails and median barriers is to safely redirect errant vehicles. Guardrail installations on shoulders prevent vehicles from crashing onto steep embankments or fixed objects, and median barriers are used between roadways of divided highways to prevent across-the-median collisions with opposing traffic. Properly designed installations accomplish the redirection of errant vehicles in such a manner as to minimize the risk of injury to vehicle occupants as well as the involvement of other vehicles in the following and adjacent traffic. Other desirable guardrail and median barrier system characteristics include minimal damage to vehicles and barrier systems and economy in construction, installation and maintenance.
There are four basic highway guardrail and bridgerail barriers in common use. One is the W-shaped corrugated, heavy gauge sheet metal barrier, horizontally placed, and supported by posts usually anchored in the ground. Another consists of steel cable strands supported by posts usually anchored in the ground. There are also a number of reinforced concrete barriers of different cross-sectional shapes. Finally, there are a number of xe2x80x9ctubularxe2x80x9d barriers, usually consisting of steel, designed either as a single or multiple horizontal rails with support posts usually anchored in the ground and/or bridge deck. These and other barrier designs are required to meet various government mandated performance standards.
The present invention is directed to certain design and performance issues regarding crash barriers, namely, redirection of impacting vehicles; deceleration of vehicle and passengers; after-impact performance characteristics of the vehicle and cross-sectional shapes of individual components and subsystems addressing issues such as aerodynamic considerations and post-crash behavior of the passengers.
Redirection of impacting vehicles is a function of xe2x80x9cattack-angle,xe2x80x9d speed, mass of impacting vehicle, center-of-gravity of the impacting mass three-dimensionally vis-a-vis the impacted barrier and the xe2x80x9cdeflectionxe2x80x9d or xe2x80x9cpocketxe2x80x9d size and shape the impact produces in the crash barrier. The maximum xe2x80x9cattack-anglexe2x80x9d dictated by U.S. and State Government performance standards is 25 degrees. This means, and addressing only the horizontal plane, the xe2x80x9ctransversexe2x80x9d vector to the barrier is 25 degrees and the xe2x80x9clongitudinalxe2x80x9d vector to the barrier is, therefore, 65 degrees. The initial friction developed by the impacting vehicle and the barrier, the transverse attack-angle increases, usually resulting in greater or deeper xe2x80x9cpocketingxe2x80x9d on the barrier by the impact vehicle. In the case of xe2x80x9crigidxe2x80x9d concrete barrier, increased initial friction usually results in the impacting vehicle developing an additional vertical-vector component, usually resulting in increased re-directional instability, i.e. roll-over.
Due to deeper pocketing and re-directional instability, the higher the friction between the impacting vehicle and the barrier, the higher the deceleration, which results in greater injury and damage being inflicted on the passengers, the vehicle and the barrier.
Post-impact performance-characteristics of vehicle and the passenger behavior are usually a question of the xe2x80x9cexit-anglexe2x80x9d or redirection of the vehicle after it leaves contact with the railing system. This is also known as the xe2x80x9cbouncexe2x80x9d. What is usually undesirable is when the vehicle develops a significant exit angle, thereby causing the vehicle to re-enter the travel-path of the highway or, worst, cross over into on-coming traffic. The bounce performance characteristics are influenced by the depth of the deflection of the rail system, or pocketing, the energy absorbed by the rail system, the energy absorbed by the deformation of the impacting vehicle and the inherent rigidity of the rail system in question. That is, if the vehicle penetrates the rail, developing a pocket that is xe2x80x9cstiff,xe2x80x9d there will be a tendency for the forward third of the pocket""s rail to become perpendicular to the path of the vehicle. This results in either too rapid a halt of the forward progress of the impacting vehicle, and/or the development of a significant exit-angle, or over-stressing the rail system to rupture.
There are a number of support post configurations in common use. Those barriers which incorporate support posts usually use xe2x80x9cwide-flangexe2x80x9d or xe2x80x9cIxe2x80x9d beam structural shapes or cold-rolled shapes formed from sheet metal usually in the cross-section of a xe2x80x9cUxe2x80x9d or xe2x80x9cCxe2x80x9d. Similar post materials are used singularly or in multiples to support mounting of items, such as signs near the travel-way of highways.
It is an object of the present invention to provide guardrails and structural support posts with reduced friction between an impacting vehicle and the barrier and post.
It is another object of the present invention to provide guardrails and structural support posts with potential additional structural strength to individual structural members of the prior art highway crash barriers and posts.
It is still another object of the invention to allow the use of a wood exterior appearance on guardrails or structural support posts without the need to use potentially environmentally harmful wood preservative treatment, since the wood cladding need not be structural and potential amounts of wood decay may improve the friction reducing feature of the cladding.
It is another object of the present invention to provide guardrails and structural support posts with an improved pleasing external appearance.
It is still another object of the present invention to provide support posts in a guardrail assembly that act as structural components of a composite structural member that would tend to add xe2x80x9cstiffnessxe2x80x9d in addition to increased load transfer ability to the post in question.
It is another object of the present invention to provide support posts in a guardrail assembly that provide a greater distribution of impact energy over the impacted area of the post, energy absorption via fracturing of the cladding, lubrication via the fractured cladding parts between the metal post and the impacting vehicle, thereby allowing the vehicle to xe2x80x9cget-pastxe2x80x9d the post and not snag as the vehicle xe2x80x9cridesxe2x80x9d the horizontal railing element.
It is still another object of the present invention to provide support posts in a guardrail assembly as a composite structural element in conjunction with the metal post with additional torque-resistance.
It is another object of the present invention to provide support posts in a guardrail assembly with resistance to the metal post elements"" potential for xe2x80x9clocalized-bucklingxe2x80x9d.
It is another objective of the present invention to provide specific aerodynamic characteristics to individual components such as rails and posts and individual subsystems such as rail/block/post systems, for purposes such as snow and/or sand issues.
It is another object of the present invention to provide a guardrail assembly which is applicable to both retro-fitting of existing barriers and posts and to new barrier and post applications.
In summary, the present invention provides a guardrail assembly for highways, comprising a horizontal rail secured to a plurality of posts. The rail includes top, bottom, front and back walls. A first wood plank is secured to the top wall. A second wood plank may be secured to the front and/or back wall. The second wood plank includes a front surface and a third wood plank is secured to the second wood plank front surface. Another plank can be attached to the back wall to provide a completely wood appearance. Plank attachments may be of glued laminated construction if for structural use, or intentionally laminated without glue to provide non-shear structural transfer characteristics between individual planks. Plank thickness can significantly vary as per design requirements. The post are also wood clad.
These and other objects of the present invention will become apparent from the following detailed description.